Cyanine pigments in electrophotographic processes

ABSTRACT

Electrophotographic processes using as the photoconductive material cyanine pigment present as very small particles.

United States Patent Champ et al. 1 June 3, 1975 [54] CYANINE PIGMENTSIN 3,041,166 6/1962 Bardeen 96/1 ELECTROPHOTOGRAPHIC PROCESSES 3,196.0117/1965 Gunther et al 96/l.l 3,250,615 5/1966 Van Allan et a1. 96/16 1Inventors: Robert Bruce p; Meredith 3,257,204 6/1966 Sus et a1. 96/l.5David Shattuck, both of San Jose. 3,507,692 4/1970 Ghys et a1 117/201Calif. 3,542,547 11/1970 Wilson 96/l.6 3,615,414 101971 L' ht ..961.6[73] Ass1gnee: International Business Machines lg I Corporation, Armonk,NY. OTHER PUBLICATIONS Kearns Kinetics and Mechanism of Photoconduc- Z2l Flled Mar 1971 t1v1ty of Metal-Free Phthalocyamne, pp. 7-12, 1963.[21] Appl. N0.: 129,637

Primary ExaminerNorman G. Torchin Assistant Examiner.lohn L. Goodrow 52US. Cl. 1511 1m. (:1 3 6353 5)? Ammey Agent Flrm'bseph Walsh [58] Fieldof Search 96/1, 1.5, 1.6, 1.7;

252/501; 117/201; 260/240, 240.1 [57] ABSTRACT Electrophotographicprocesses using as the photocon- 1 References Cited ductive materialcyanine pigment present as very small UNITED STATES PATENTS Particles-2,663,636 12/1953 Middleton 96/15 8 Claims, N0 Drawings CYANINE PIGMENTSIN ELECTROPHOTOGRAPHIC PROCESSES BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to electrophotographic processesand photoconductive plates used therein. In particular it is concernedwith plates comprising certain cyanine pigments.

2. Description of Prior Art US. Pat. No. 3,542,548 lists certain cyaninepigments, structurally different from those of the present invention.The pigments of that patent are not photoconductive, but are used assensitizers for photoconductors.

US. Pat. No. 2,663,636, concerned with a binder type photoconductiveelement, suggests micropulverizing organic photoconductors.

In other places in the prior art, milling of photoconductor to obtainsmall particle size is also shown.

No prior art reference of which we are aware, however, suggests theadvantages obtained in the present invention, which involves the use ofcertain selected cyanine compounds as very small sized particles inelectrophotographic reproduction processes.

SUMMARY OF THE INVENTION The cyanine pigments of the present inventioninclude those having the formula wherein R is selected from thegroupconsisting of hyl, ethyl and allyl, X is selected from the groupconsisting of the chloride, bromide and iodide ions, Y and Z are eachselected from the group consisting of O, S and Se, and A is selectedfrom the group consisting of hydrocarbon chains having the formula CH :A

and

microns in diameter, and preferably less than 1 micron in diameter. theyare very effective photoconductors.

There are several well known electrophotographic reproduction processesin current use. They differ in the particular way in which they arecarried out, particularly the sequence in which electric charging(usually with a corona) and illumination are carried out. Allelectrophotographic reproduction processes, however, involve the processstep of selectively rendering portions of a photoconductor electricallyconductive by selective exposure to light. The pigments of the presentinvention are useful in all such processes.

Compounds of the above formulas may all be prepared by well knownprocedures picking the properly substituted starting materials in eachcase, and carrying out the synthesis by methods in accordance with theteachings of the prior art.

It must be emphasized that the particles of pigment are not dissolved;i.e., they are not present as single molecules in a solution. Ratherthey are present as polymolecular aggregates. The use of the wordpigment to describe the materials is in accord with this fact, since theword pigment in the art is usually used to describe a colored particlewhich is not in solution, as contrasted to the word dye, which is usedto describe colored material which is in solution.

As mentioned previously, the pigment size should be less than 5 micronsin diameter. Preferably the pigment size is less than about 1 micron indiameter. Furthermore, there is some evidence to suggest that in atleast some cases it is advantageous that the particle sizes are close touniform.

In accordance with the present invention, the pigments may be used inthe form of a thin layer on a conductive substrate. This layer may beovercoated with a charge transport layer. Systems of this sort aredescribed in US. Pat. No. 3,598,582, issued Aug. 10,

Alternatively, the pigments may be present in a binder medium, which maybe either photoconductive per se or not photoconductive per se. Thereare many binders known to the prior art as being useful in the making ofphotoconductive plates. They include numerous resins and the like. Manysuch materials are mentioned, for example, in US. Pat. Nos. 3,121,006and 3,121,007. Among the resins found useful in the present invention,polyesters have been particularly outstanding, for example. Mylaradhesive 49,000, which is duPonts trademark for a 60/40 copolymer ofethylene terephthalate and ethylene isophthalate. Polyketones are alsouseful, e.g., PK 252, Union Carbides trademark for a polyketone. It isnot, however, necessary that the binder be a resin. For example, US.Pat. No. 3,406,063 lists non-polymeric coating-forming materials whichmay also be used in the present invention. It should also be mentionedthat sucrose benzoate gives especially outstanding results when used asa binder in the present invention.

To increase the photoconductivity of some of the above-describedphotoconductive pigments, there may be incorporated in the pigmenteither a sensitizer or an activator which is also known as an electronacceptor or, in some cases, when the photoconductor is an electronacceptor, an electron donor. Examples of such dye sensitizers andactivators are set forth in US. Pat. Nos. 3,037,861, 3,169,060, and3,287,113. In addition. when it is desired to have the photoconductiveelement exhibit persistent conductivity, the dye sensitizer andactivator combinations described in U.S. Pat. No. 3,5 12,966 may be usedin the preparation of such photoconductive elements.

The milled pigment was mixed at 10% by weight concentration with abinder of Mylar adhesive 49,000 in THF. This mixture was coated on roughstock aluminum at a 5 mil wet gap and cured for minutes at From aboutone percent, up to about 50%. by weight 5 100C. The electrometer datawere as follows: using a f h blnder y be p g t, depending p e par- 1.47Neutral Density Screen and opal glass, the sensitlcular pigment a the pr i l r bindertivity (T /z) in negative mode was 0.18 seconds, and

y of the Plgmehts useful the Present invention the charge acceptance 500volts, also in the negative have been listed in the Colour Indexpublished jointly d by the Society of Dyers and Colourists in Englandand l0 the American Association of Textile Chemists and Col- EXAMPLE 2Ofists. Lowell, M355, Second Edition, 1956- In some At a 10% solidslevel. Pigment l was Spex-milled in cases below, they are referred to bytheir Color Index THF f 30 i t Th milled pigment was then number, addedto Mylar adhesive 49000 in THF at a 50% level In the examples below,when the expression Full of addition. This dispersion was coated (wetgap of 15 Tungsten or F.T. is used, it means that the light source i oal minum rough stock subbed with a 1 mia a tungsten l g p, 75 W 28Volts, at cron thick layer of Milvex 4000 polyanide resin and i n f ppry 15 centimeters cured for 10 minutes at 100C. (Milvex 4000 is GeneralWhile the Invention Wln be particularly Shown and brand of acidndiamineopolymer polyam described with reference to preferred embodiments id yThed d were; CA, (+)500 volts; thereof, it will be understood by thoseskilled in the art i i i (T 2 Seconds (1,16 ND 0,0). This that Various.Changes in the form and details m y be sensitivity is approximately 6times that of the organic made therein without departing from the spiritand photoeonduemr r ntl in commercial use. scope of the invention.

LE EXAMPLES 5 3 7 S Pigments with the o owing structures were pex-EXAMPLE 1 mixer milled in THF at 10% solids for minutes. They Thepigment used in this experiment was 3,3'-diethyl were then added at 20%level of addition by weight to benzothiazolium dicarbocyanine iodide,hereinafter 30 a hot melt of trinitrofluorenone (TNF), thoroughly calledPigment I. mixed and coated by doctor blading at a thickness of A 20%solid mix of Pigment I in tetrahydrofuran 10 microns on a rough stockaluminum substrate. (THF) was Spex-milled for 30 minutes with steelballs. The electrometer data were as follows:

C.A. T 1 2 Ex. 3 (Full Tungsten) C H $6 5 Sev KI ca: c CH :Q I 150v. 0.3Sec.

N N I l Z 2 5 Se i 3 Se Di) 1' 800V. 0.15 Sec.

| C2H5 CZH5 S s @i cH=cn ca; jg I 300v. 0.15 Sec.

N N' l V. 0.2 Sec.

CH: CH CH N I C H EXAMPLES 8-11 The cyanine pigments listed below wereSpex milled in 10% solutions in THF. The milled pigments were each addedto mixtures of Mylar adhesive 49,000 and TNF in THF and the mixturesmilled together overnight with the addition of a quarter percent byweight C.A. T l/2 (Full Tungsten) 300V. 0.25 Sec.

200V. 0.25 See.

of silicone lubricant as a flow aid. The weights of the TNF and theMylar adhesive 49000 were equal. The

weight of the cyanine pigment in each case was 10% of the total solids.The final mixture was coated with a doctor blade on a rough stockaluminum substrate. The plates were cured overnight at 55C. Theelectrometer results (full tungsten) were as follows.

C.A. (Volts) T l/2 (Sec) @K CH I) 1' 520 870 3.5 1.5

N N l I cn =cncH= Us I 420 520 4.0 1.7

N N l C.A. '1 1/2 (Volts) (Sec) CHzCH cH I: I

N N l CHCH=CH CH-CH=CH EXAMPLE 12 tained was coated on a matte finishaluminum plate.

The photosensitivity of the plate was approximately times that of acommercial organic photoconductor with a charge acceptance of +800volts.

EXAMPLE 13 A plate was prepared by adding 3,3"-diethyl-9- methylthiacarbocyanine iodide which had been milled to very small particlesize at a 5%by weight concentration to a solution of polyvin-ylcarbazolecontaining 1% by weight TNF. The mixture was coated on matte finishaluminum. The electrometer data were: CA 450 volts mode), 780 voltsmode) T /2 0.42(+) and O.50().

What is claimed is:

1. In an electrophotographic reproduction process which comprisesselectively rendering portions of a photoconductor electricallyconductive by selective exposure to light, the improvement according towhich the photoconductor comprises polymolecular aggregates less thanfive microns in size'of a pigment having the formula:

@iw afio wherein R is selected from the group consisting of methyl,ethyl and allyl. X is selected from the group consisting of thechloride. bromide and iodide ions, Y and Z are each selected from thegroup consisting of O, S and Se, and A is selected from the groupconsisting of hydrocarbon chains having the formula C--CH,=cH--c=cH--cH-.=

I Q Q and wherein Q is selected from H, CH and CH 2. A process asclaimed in claim 1 wherein the particles of pigment are less than lmicron in size.

3. A process as claimed in claim 1 wherein the pigment is in the form ofa layer overcoated with a charge transport layer.

4. A process as claimed in claim 1 wherein the pigment is dispersed in abinder.

5. A process as claimed in claim 4 wherein the binder comprisestrinitrofluorenone.

6. A process as claimed in claim 4 wherein the binder comprises sucrosebenzoate.

7. A process as claimed in claim 1 wherein the pigment is 3,3-diethylbenzothiozolium dicarbocyanine iodide.

8. A process as claimed in claim 7 wherein the pigment is dispersed in abinder comprising sucrose benzoate.

1. In an electrophotographic reproduction process which comprisesselectively rendering portions of a photoconductor electricallyconductive by selective exposure to light, the improvement according towhich the photoconductor comprises polymolecular aggregates less thanfive microns in sIze of a pigment having the formula:
 1. IN ANELECTROPHOTOGRAPHIC REPRODUCTION PROCESS WHICH COMPRISES SELECTIVELYRENDERING PORTIONS OF A PHOTOCONDUCTOR ELECTRICALLY CONDUCTIVE BYSELECTIVE EXPOSURE TO LIGHT, THE IMPROVEMENT ACCORDING TO WHICH THEPHOTOCONDUCTOR COMPRISES POLYMOLECULAR AGGREGATES LESS THAN FIVE MICRONSIN SIZE OR A PIGMENT HAVING THE FORMULA:
 2. A process as claimed inclaim 1 wherein the particles of pigment are less than 1 micron in size.3. A process as claimed in claim 1 wherein the pigment is in the form ofa layer overcoated with a charge transport layer.
 4. A process asclaimed in claim 1 wherein the pigment is dispersed in a binder.
 5. Aprocess as claimed in claim 4 wherein the binder comprisestrinitrofluorenone.
 6. A process as claimed in claim 4 wherein thebinder comprises sucrose benzoate.
 7. A process as claimed in claim 1wherein the pigment is 3,3''-diethyl benzothiozolium dicarbocyanineiodide.